Cast aluminum magnetic ferrite attenuator and the like



June 1965 J. l. STILLMAN ETAL 3,

CAST ALUMINUM MAGNETIC FERRITE ATTENUATOR AND THE LIKE Original Filed Dec. 2, 1958 3,191,267 CAST ALUMINUM MAGNETIC FERRITE ATTENUATGR AND THE LHKE Jerome I. Stillman and Robert Y. Scapple, Los Angeles, Calif., assignors to Hughes Aircraft Company, (Zulver City, Calif., a corporation of Delaware Original application Dec. 2, 1958, Ser. No. 777,649. Divided and this application Sept. 20, 1961, Ser. No.

6 Claims. (Cl. 29-1555) This is a division of our copending application Serial No. 777,649 filed December 2, 1958, now abandoned.

The present invention relates to a method of bonding a ferrous metal to an aluminous metal to form a tight molecular bond between the two metals, and particularly to integrally joining iron pole pieces to an aluminum alloy body of a waveguide device such as a magnetic ferrite attenuator, for example.

Although the invention will be more particularly described herein as applied to magnetic ferrite attenuators, it will be understood that it is generally applicable to waveguide devices, particularly microwave ferrite-loaded waveguide devices, such as microwave gyrators, modulators, isolators, phase shifters, switches, duplexers, etc., in addition to attenuators.

Magnetic ferrite attenuators of the type especially under consideration include a generally elongate tubular waveguide body section, terminal flange members and magnetic iron pole pieces mounted in the walls of the body section and joined by a permanent or electro-magnet to induce a magnetic field in the waveguide. The ferrite materials are cemented to the pole pieces on the interior of the body section. The body section and the terminal flanges of the attenuator have, in the past, been made from brass sheet stock. This involved numerous, uneconomical cutting, slotting, machining and brazing operations which resulted in the employment of many operating steps involving many pieces of material and wastage of material and time. Furthermore, brass is a relatively expensive material and its use imparts an objectionable amount of weight to the attenuator. Its density is about three times that of aluminum.

Accordingly, it is an important object of this invention to provide an efficient and economical method of making the body and flange portions of a magnetic ferrite at tenuator.

Another object of this invention is to provide a lightweight, magnetic ferrite attenuator wherein the body section and terminal flange portions are made of a light metal, such as an aluminum alloy.

The use of aluminous metals in the attenuator body section poses a very difficult problem of forming pressuretight joints between the iron pole piece and the walls of the aluminum body section. Furthermore, to reduce the number of pieces of material handled, the wastage of material, and the number of operating steps employed during the construction of the waveguide body section and flanges, it was decided to investment-cast the body section and flanges as an integral unit. Investment-casting was selected to meet the requirements of precise dimensional tolerances and smooth interior surface finish of the attenuator. Difiiculties were experienced, however, when attempts were made to cast the aluminum body section around the iron pole pieces because the desired pressure-tight joints between the pole pieces and the walls of the waveguide body section were not attained. Metal oxide appeared to form on the iron, and during solidification and contraction of the aluminum casting metal the necessary bonding alloy formation did not take place at the joints between the pole pieces and the walls of the waveguide body section. Centrifugal and gravitational United States. Patent 0 "ice Patented June 29,

casting procedures did not solve this bonding problem.

It is, therefore, a further object of this invention to provide an efficient method of making a pressure-tight bond between the iron pole pieces and the walls of an aluminum alloy body section of a magnetic ferrite attenuator.

These and other objects will become apparent from the following description which is given primarily for purposes of illustration and not limitation.

Stated in general terms, the objects of this invention are attained by providing a method of bonding a ferrous metal member, such as a pole piece, to an aluminous metal member, such as a waveguide body section, by first providing the ferrous member with a tin plating, positioning the two members in relationship to each other to form the desired joint, such as with the aid of a dip brazing fixture, applying a suitable brazing alloy to the joint, immersing the resulting assembly in molten flux to braze the plated ferrous member or pole piece to the aluminous member or waveguide body section, and recovering the brazed assembly from the molten flux. The recovered assembly is cleaned and finished in the usual manner known in the art. The method of this invention is, of course, especially adapted for brazing magnetic iron pole pieces into the walls of an aluminum alloy waveguide body section to produce a light-weight, aluminum microwave ferrite loaded waveguide device, such as a magnetic ferrite attenuator, wherein the iron pole pieces are tin coated and molecularly bonded to the Walls of the aluminum alloy waveguide body section to form pressure-tight joints between the waveguide body section and the pole pieces.

A more detailed description of a specific embodiment of the invention is given with reference to the accompanying drawing, wherein:

FIG. 1 is an isometric view showing a cast aluminum waveguide section including integral terminal flanges;

FIG. 2 is a similar view, partly in section, showing an assembly of coated iron pole pieces dip-brazed into slots in opposed walls of the cast waveguide section;

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 4 and showing an assembled, encapsulated waveguide unit including a permanent magnet and ferrite plates attached to the inner ends of the pole pieces; and

FIG. 4 is a longitudinal sectional view taken along line 4-4 of FIG. 3 showin the encapsulated assembly.

A tubular waveguide body section 10 with a flange 11 and 12 on each end thereof, respectively, was cast as an integral unit in a precision investment casting operation to provide a smooth surface and accurate dimensions to the casting. The aluminum casting alloy employed was one of a type suitable for dip brazing, such as one containing about 6.5 percent zinc, about 0.5 percent copper and about .5 percent magnesium in addition to aluminum. The casting was done by making a wax pattern which included the waveguide section and the two flanges. Suitable slots, dimensioned for forming slots 13 and 14 designed for later receiving the iron pole pieces 15 and 16, respectively, were provided in the wax pattern. The slotted wax pattern was placed into a crucible and covered with a suitable investment slurry. The crucible then was baked in a furnance to evaporate the moisture from the slurry and to form a mold from which the molten wax was expelled and burned off. After baking, the crucible was removed from the furnace and a quantity of a suitable molten aluminum alloy was immediately poured into the hot mold. The resulting investment casting was immersed in an alkaline cleaning bath, rinsed and then immersed in an etching bath. The etched casting was rinsed thoroughly and air dried.

The iron pole pieces 15 and 16 first were tin-plated to a thickness of about 0.0002to about 0.0004 inch by an electroplating method. The resulting tin plate was fused A suitable brazing alloy, preferably having a composi-,

tion'as follows: ll.0l3.0% Si, 0.3%. Cu,'0.80% Fe, 0.2% Zn, 0.10% Mg, 0.15% Mn, balance Al, and having.

the approximate melting range ofabout l0701080. F., was applied'in generous amounts to thegjoints to be brazed.

Thefixture and assembled parts-were placed into a preheat furnace operating at about 450 F. The assembly was.

kept in the furnace until it reached the furnace tempera.-

ture to evaporate moisture and minimize distortion in the: subsequent brazing operation. 1 Thefpreheat' temperature should not exceed about450" F. to prevent burn-oif'of the tin plate or excessive diffusion'into the iron.

As soon as the assembly reached the furnace. tempera-,

ture, it was: removed from the furnace and submerged in.

a bath of molten flux consisting of lithium chloride. and aluminum fluoride maintained at 1100915? F. The chloride content of the bath was maintained from 52.8 to

arenas"! 54.8 percent and the fluoride content from 3.4 to. 4.8 per cent by appropriate addition of the respective salts tothe bath. The assembly was submerged slowly and steadily. After a few'minutes of brazing time expired, the fixture containing the assembly was slowly raised from the bath to alloy suflicient time for the brazing alloy to set.

The fixture and parts then were allowed to air coolto about 275 F. before quenching in hot water. Remnants of the flux were removed from the quenched assembly by thoroughly rinsing it in circulatinghot water and other foreign matter was cleaned from the resulting integral assembly of waveguide body section 10, flanges 11 and 12. and pole pieces 15 and 16. 1 I V a The brazed joints showed no signs of leakage when an internal pressure of 45 p.s.i.g. was applied to the assembly while submerged in water. The resulting assembly was.

finish machined precisely to the desired dimensions, and after additional-cleaning, was provided with a protective chromate conversion finish coating. ,An Alnico V magnet 17 was assembled around the waveguide body section 10 onto the pole pieces 15 and 16, .as bestshown in FIGS. 3'

and 4. The ferrite plates 18. and 19- were attached to, the

pole pieces 15 and 16, respectively, on the inside walls of the waveguide body section 10. The resulting assembly was encapsulated, asshown at 20, and painted and stenoiled.

Photomicrograph examinations of the brazed "joints formed by themethod described immediately hereinabove showed that an intermetallic alloy interface was formed at the joint between the iron pole'pieces and the aluminum the aluminum brazing alloy can react rapidly and uni-' forrnly with the iron pole'pieces during the brazing operation to-form the observed'strong, molecular, pressure-' tight bond, which is a feature of; this invention. The photomicrographs show brazed joints free of oxides or voids between the iron pole pieces andthe brazing alloy.

On" the other hand, if an aluminum alloy waveguide 7 body section is cast directly around an unplated' iron. pole piece, inv accordance with known-prior art procedures; photomicrographs of the joint area show that oxides form on the ironpole pieces. Extensive experiencewith such direct casting prior art. procedures showed that during solidification and contraction of the molten aluminum casting metal, no alloy formation took place between the iron and the aluminum of the casting metal. As a result, satisfactory pressure-tight bonds were not obtained while using the prior art direct casting methods.

In the specific description given above, it was stated that the tin plate was applied to the iron pole piecesby an, electroplating method and the resulting tin plate was fused to produce an adherent,non-porouscoating. This procedure canbe modified by tin-plating the pole pieces by immersing them in a hot tin dipping bath and placing them immediatelyin .a heatedcentrifuge and centrifuging the hot pole piece-s before the molten tin solidifies thereon. The resulting centrifugal action evenly distributes the molten tin over the pole pieces to produce an adherent, continuous'coating. Alternatively, the'tin can be applied to the ironpole pieces by simply dipping them'in, a hot; tin dippingv bathin a conventionalmanner; Instead of hot tin dipping or tin electroplating, vapor depositionof tin, or any other suitable method for applying the tin to the iron pole pieces can be employed.

The aluminum alloy waveguide was described above as being made by an investment-casting procedure. However, the tubular waveguide body section 10 can be made' by ex-trudinga suitable aluminum alloy bymethods knownin the art. The terminal flangesll and 12 can 'be machinedfrom plate stock or made in any other'suitable' manner.

The terminal flanges are assembled on the ends of the extruded waveguide body section at .the same time that the iron pole'pieces 13 and 14 are inserted into the slots 13 and 14 of the body section 10. Brazing alloy is placed around the joints between theflange-s 11 and12 and the ends of the body section 10 at the same time that it is placed aroundthe joints between the body section and the pole pieces 15 and 16. When the pole pieces are dip brazed to the body'section 10, the terminal flanges also will'be dip brazed to the ends. of the body section to form an. integral, unitary assembly of the pole pieces. and the terminal flanges on, thebody' section and thus produce the magnetic ferrite attenuator described above. 7 a 1 a a i The present invention has beendescribed and illustrated hereinabove at some length. It will now be' apparent to persons skilled in the. art that various modifications andcombinations of various features disclosed. or suggested may bernade andva rious equivalents may be substituted without departing from the. spirit of this invention. 7 Accordingly, the .scope' of the invention is intended to bev limited only by the spirit and scope of the appendedclaims. I M What. is claimed is: g t j I Y 1. Themethod of making a waveguide deviceincludingan aluminous'metal .waveguiderand. ferrousmetal pole pieces which; comprises the steps of tin-plating. the pole pieces, fusing the. tin plate. on the pole pieces to form an adherentcontinuous. plating thereon, mounting the plated pole pieces'in position inthe waveguide to. form jointsto' be brazed between the. waveguide. and the pole pieces; ap-

plying a brazing alloy to'the joints,l immersing the resultmgassembly in molten flux to braze the pole. pieces to the-.-

waveguide, and recovering .the. brazed assemblyfrom the! molten flux.

' 2; The method, of making a waveguide device including an aluminous metal'w'aveguide and ferrous. metalpolev recovering the brazed assembly fronitheE-molte'n flux.

3. A method of making a waveguide device including an aluminous metal waveguide member and ferrous material pole pieces which comprises the steps of investmentcasting the waveguide member, tin-plating the pole pieces, fusing the tin plate to form an adherent continuous plating, mounting the plated pole pieces in position in the waveguide member to form joints to be brazed between the waveguide and the pole pieces, applying a brazing alloy to the joints, immersing the resulting assembly in molten flux to braze the pole pieces to the waveguide and recovering the brazed assembly from the molten flux.

4. The method of making a waveguide device including an aluminous material waveguide member and ferrous metal pole pieces which comprises the steps of investment-casting the waveguide member, tin-plating the pole pieces, immersing the tin-plated pole pieces in hot oil to fuse the tin plate and form continuous adherent plating on the pole pieces, recovering the tin-plated pole pieces from the hot oil, mounting the plated pole pieces in position in the waveguide member to form joints to be brazed between the waveguide and the pole pieces, applying a brazing alloy to the joints, immersing the resulting assembly in molten flux to braze the pole pieces to the waveguide, and recovering the brazed assembly from the 5. The method of making a waveguide device including an aluminous material waveguide member containing a tubular body section and terminal flanges, and ferrous metal pole pieces which comprises the steps of extruding the body section, forming the terminal flanges, tin-plating the pole pieces, fusing the tin plate to form an adherent continuous plating, mounting the terminal flanges on the ends of the tubular body section, mounting the plated pole pieces in position in the waveguide member to form joints to be brazed between the waveguide and the pole pieces, applying a brazing alloy to the joints and to the terminal flanges, immersing the resulting assembly in molten flux to braze the pole pieces and the terminal flanges to the waveguide body section, and recovering the brazed assembly from the molten flux.

6. The method of making a waveguide device including an aluminous material waveguide member containing a tubular body section and terminal flanges, and ferrous metal pole pieces which comprises the steps of extruding the body section, forming the terminal flanges, tin-plating the pole pieces, immersing the tin-plated pole pieces in hot oil to fuse the tin plate and form a continuous adherent plating on the pole pieces, recovering the tin-plated pole pieces from the hot oil, mounting the terminal flanges on the ends of the tubular body section, mounting the plated pole pieces in position in the waveguide member to form joints to be brazed between the waveguide and the pole pieces, applying a brazing alloy to the joints and to the terminal flanges, immersing the resulting assembly in molten flux to braze the pole pieces and the terminal flanges to the waveguide body section, and recovering the brazed assembly from the molten flux.

References Cited by the Examiner UNITED STATES PATENTS 699,592 5/02 Thompson 29502 2,776,412 1/57 Sparling. 2,809,423 10/57 Hanink 29-504 X 3,041,554 6/62 Blasberg et al. 333-242 3,048,913 8/62 Ball 29l55.5 3,049,680 8/62 Krogh 333-24.2 3,063,027 11/62 Hughes 33324.2 3,063,029 11/62 Hughes 333-24.2 3,099,806 6/63 Blasberg et a1 333-242 OTHER REFERENCES Modern Metals, April 1948, pp. 13-15.

WHITMORE A. WILTZ, Primary Examiner.

JOHN F. CAMPBELL, Examiner. 

1. THE METHOD OF MAKING A WAVEGUIDE DEVICE INCLUDING AN ALUMINOUS METAL WAVEGUIDE AND FERROUS METAL POLE PIECES WHICH COMPRISES THE STEPS OF TIN-PLATING THE POLE PIECES, FUSING THE TIN PLATE ON THE POLPOLE PIECES TO FORM AN ADHERENT CONTINUOUS PLATING THEREON, MOUNTING THE PLATED POLE PIECES IN POSITION IN THE WAVEGUIDE TO FORM JOINTS TO BE BRAZED BETWEEN THE WAVEGUIDE AND THE POLE PIECES, APPLYING A BRAZING ALLOY TO THE JOINTS, IMMERSING THE RESULTING ASSEMBLY IN MOLTEN FLUX TO BRAZE THE POLE PIECES TO THE WAVEGUIDE, AND RECOVERING THE BRAZED ASSEMBLY FROM THE MOLTEN FLUX. 